Foetal membranes bulging into the abdominal cavity is a unique initial manifestation of silent or complete uterine rupture during pregnancy. Since silent uterine rupture has potential risk for complete uterine rupture, which leads to acute life-threatening complications for both the mother and baby, it is difficult to determine whether to manage expectantly or surgically, including repair of the uterine wall or termination of the pregnancy, especially in the early second trimester. We present here a case of a herniated amniotic sac with overstretched uterine wall of the fundus presenting as silent uterine rupture, which was incidentally detected on routine ultrasonography at 18 weeks' gestation in a 38-year-old primigravida with a history of myomectomy for diffuse uterine leiomyomatosis. Magnetic resonance imaging examination revealed that the myometrium thickness was fully maintained at the site of the foetal membranes ballooning. The pregnancy was therefore managed expectantly and continued to successful delivery at 30 weeks' gestation. The precise assessment of the uterine wall may be essential to manage a herniated amniotic sac presenting as silent uterine rupture and to optimise the outcome of the pregnancy. We review all cases of a herniated amniotic sac out of focally overstretched uterine wall before 34 weeks' gestation.